1. Technical Field
The present invention relates to Localized Metal Precipitate Formation (hereafter referred to as LMPF) and the corresponding metallization depletion, and more particularly, to methods for suppressing and monitoring LMPF, and suppressing interconnect depletion in semiconductor processing.
2. Related Art
During the process of fabricating chips on a semiconductor wafer, there may be at least two electrically isolated metal wires exposed to the manufacturing environment at the surface of the wafer. Due to photo and/or other forms of excitation, one of the two metal wires (hereafter referred to as the first wire) may be at a higher electrical potential than the other metal wire (hereafter referred to as the second wire). When the wafer undergoes a CMP (Chemical Mechanical Polishing) step, during which the wafer is exposed to an ionic solution, some metal atoms (M) of the first wire dissolve in the solution and become ionized (M−>Mn+). As a result of the electrical potential difference between the first and second wires, some of these ionized atoms move in the solution from the first wire towards the second wire, and redeposit as localized metal precipitates (LMP) at the second wire (Mn+→M). These LMPs may cause a short-circuit in the devices on the wafer, which would degrade or destroy the ability of these devices to perform their intended function. Also, in some situations, the metal ions that dissolve into the ionic solution are drawn from a very small area of the first metal wire, resulting in localized removal of metal in that wire, often referred to as depletion or erosion of the metal. This localized loss of material from the first wire degrades the current carrying capability of the line and can lead to premature metallization failure.
Therefore, there is a need for a structure to prevent such localized metal precipitate formation and the corresponding metallization depletion. Also, there is a need for a method for forming the structure. There is also a need for a method for monitoring such LMPF.